How to Store Seeds and Test Germination Rates

Storing Seeds

Proper storage conditions for seeds are essential to maintain viability and good germination at planting time. Seeds should be kept dry and cool.  A sealed glass jar can keep excess moisture out and protect seeds from pests like mice or insects. Store jars in a cool, dry location such as a cool closet, root cellar, or refrigerator. Test the germination rate on the seeds about one month prior to planting.

If you collect the seed from your garden, ensuring the seed is dry after cleaning and processing is the most important step to successfully storing seed. Place seed in labeled envelopes. In a separate envelope, place an equal amount of silica gel. Place both envelopes into a clean glass jar and seal shut. After one to two weeks, the seed should be sufficiently dry for storage. Remove the silica gel and return the envelope to the glass jar. Some seed may dry sufficiently utilizing a fan in a seed drying cabinet. Avoid the use of a food dehydrator to dry seed as they usually get too warm and damage the seed.

Test Germination Rates of Seed

Seed left in storage will decrease in quality over time. Just looking at the seed will often give an indication of seed quality. Seeds that are usually smooth and round or plump will germinate poorly if they are pocked or wrinkled. Peas, corn, and many other seeds are normally wrinkled but may not look as good as they should.

If the seed does not look fresh or is more than one year old, it is beneficial to test the germination rate.  If germination rates are low, you will benefit from sowing more seed to ensure that enough seedlings germinate and grow to have the number of plants you need for your garden.  When germination rates are exceptionally low, it is often more productive to discard the old seed and buy fresh seed packaged for that current growing season.

To run a germination test:

1. Count out at least 20 randomly picked seeds (50 is better, 100 is best).
2. Spread the seeds on several layers of premoistened paper toweling and roll them up in the paper so the seeds stay separated from one another.
3. Place the roll into a plastic bag and keep it in a warm place (70° to 80° F). Remember to label each roll with seed type.
4. Check the seeds in two or three days, and every day thereafter for a week or so.
   • When a root or cotyledon protrudes through the seed coat, the seed has germinated.
5. When some seeds have sprouted, and a one-week wait indicates that no more are about to emerge, you can calculate your rate of germination.
6. Divide the number of seeds germinated by the number of seeds tested to find out your germination percentage.

For most species, a germination rate of 90% or more is very good.  Some species may have lower germination rates, but because the seed is small and/or abundant, a rate of 70% to 80% is perfectly acceptable.  Other species may naturally have lower germination rates.  Seed is often sold with a germination rate at the time of packaging indicated on the package.  If the germination rate is still relatively close to the original rate, then it is worth sowing.  For nearly all species, a germination rate of 50% or lower is too low to be worth using and the seed can be discarded and replaced with newer seed.

If handled very carefully, germinated seeds from the germination test may be planted in the garden (if the planting time is right) or in cell packs and peat pots for further growth. If the root or shoot is damaged in the transplanting process, the plant will not survive.

Seed Viability

How the seed was stored will play a major role in its viability.  When stored well, some seed will remain viable (and have good germination rates) for longer periods of time than others.  

Below is a guide to give you an idea of how long you can expect certain vegetable seeds to remain viable when stored under optimal conditions.  This guide does not replace a germination test.  It can help you determine if seed is too old to even spend the time doing one.  For seed much older than what is outlined below, discard the seed and buy new rather than spending time performing a germination test.

Length of Time Vegetable Seeds Can be Expected to Remain Viable if Stored Properly

* The number of years listed assumes ideal storage conditions.  The germination rate will still decrease each year, but when within this time range will still be at an acceptable level.